Before I sorted down my flock into breeding pens I had 2 roos for 8 girls. No real issues until they decided mating season was full swing. Had about 100% fertility with 2 at all times. Fertility may have dropped a bit, but seperated down to 1:3 ratio for the less dominate and 1:4 for the other. Still great fertilty. With the breeding set up I have now, all large breeds except 1 LH cross. its about 1:4 ratio in all pens and no issues with over mating as of yet and its been roughly a month. I have added 2 more roos and each have 4 hens. These are breeding projects.
1 roo is also short a hen since she went broody. This roo, my most dominate is also sharing a coop with 6-8 guineas, male and female (6 atm normally 8 have a couple broodies) and a pair of rouen ducks. Of which the drake, a young bird puts ALL other birds in place around his mate. 2 of my roos are prolly at least 4 years old though. Every flock will be different, as well as every breed and indavidual bird in the flock. If it works don't worry about change. If it doesn't find what works best for your birds.